Second, consider getting a critique before you decide whether you need to pay for a full copyedit. I (and probably many other editors) will read your manuscript and write a several-page critique for much less than the cost of a line-by-line edit, and if your mechanical skills are reasonably good, this may be sufficient to help you get it into adequate shape for your publication plans.
Inspect the spine of the book and look for a smaller name under the author. Turn the book over and look at the spine—the thin side of the book where the pages are bound to the cover. If there are multiple names on the spine of the book, they are always ordered with the author’s name first, and the editor’s name after it. On most books, the editor’s name will be smaller so that a passerby can quickly tell who the author is.
If you know you are sensitive to changes, or that you only want edits that correct what’s wrong (and not subjective edits beyond that), tell the editor so. This kind of information is invaluable, and will prevent frustrations and misunderstandings. That said, don’t suggest this if you’re open to your work being better. Editors will bring your work to a whole other level if you’re able to loosen your grip on any notion that your creative expression is under attack when an editor makes changes to your work. The most successful authors are edited multiple times over.
Obviously there is a big difference. I actually started with screenplays (with some mild success) partly due to hearing that as long as you have a good story, the grammatical errors won’t be a big deal. Well, that was not true. Maybe if a producer liked the story or I was already established but every contest I entered always came back with feedback about the grammatical errors. Even if I won or placed as a finalist, I always received critique on that. Very little is spelling error, it was more about structure, etc.